Lubricants containing benzylureas



United States ate This application relates to lubricants possessing superior antioxidant and anticorrosive properties. More particularly, it relates to lubricant compositions inhibited from oxidation by particular benzyl-substituted ureas.

Compositions which are employed in lubrication of modern automobile engines, machinery, etc., are becoming increasingly subject to attack by oxidation under the severe operating conditions encountered in these machines. This is due to the increased speeds and correspondingly increased temperatures at which the equipment is operated. When the compositions are attacked by oxidation, a resulting buildup in oxidative products in the lubricants often results in increasing wear upon the parts being lubricated with resultant early failure of the equipment.

The increased corrosivity is especially pronounced in the case of metal-ion containing lubricants, such as automatic transmission fluids, as the transmissions which are being lubricated as Well as being provided with friction control agents are operated at increasingly higher speeds and temperatures. Other materials which are severely affected by these facts are the metal-soap gelled greases, particularly lithium soap greases which are often employed in high temperature applications because of their high dropping points, etc.

It is thus desirable to provide additives for oleaginous lubricants such as those illustrated which will successfully inhibit oxidation of the lubricant. It is also desirable that the materials employed as additives be non-toxic so as to facilitate safe handling and non-volatile so that they will remain in the lubricants at elevated temperatures.

It has now been found that improved lubricant compositions resistant to oxidation can be compounded from a major portion of an oleaginous lubricant and a minor portion sufiicient to inhibit oxidation of a benzyl-substituted urea of the formula:

in which R is phenyl or an alkylphenyl radical substituted by alkyl radicals containing from 1 to 30 carbon atoms and having a total of not more than 90 alkyl carbon atoms, and R R and R are hydrogen or hydrocarbyl radicals of l to 30 carbon atoms.

Thus, the antioxidant materials of this invention are substituted ureas that derive the main of their antioxidant effect from the benzyl grouping attached to at least one the urea nitrogens. In the preferred materials, R is an alkyl phenyl group. R may be alkyl or arylv However, in the preferred materials, R is hydrogen, as the hydrogen appears to contribute in some degree to the antioxidant activity of the compound. R and R may be alkyl, alkylaryl or aryl, etc. However, in a preferred form, one is hydrogen and the other a phenyl or substituted phenyl radical. The end of the molecule on which R and R are substituted appears to contribute little to the antioxidant effect, but these groups may be varied to adjust the solubility of the additive in the lubricant base.

It will be found in general that R or R are preferably aryl, because in preparation of the compound it is usually necessary to employ an isocyanate of the radical, and the alkyl materials are quite toxic while the aryl materials are relatively inert or non-toxic.

Illustrative materials which may be used include benzyl aryl ureas such as 1-benzyl,3-phenylurea, l-benzyl,3,3,- diphenylurea, etc., 1-benzyl,3-alkyl,3-arylureas such as l-benzyl,3-rnethyl,3-phenylurea, and 1-benzyl,3-ethyl,3- tolylurea, etc. The phenyl ring of the benzyl group is preferably substituted by alkyl groups which may have up to 30 carbon atoms in each with a total of up to alkyl carbon atoms. Thus, materials may be used such as 1-(4- methyl,3-ethylbenzyl) 3-arylureas. The substitution on the No. 3 nitrogen may also be by a benzyl or substituted benzyl group.

The antioxidant materials are included in the compositions in amounts sufficient to inhibit oxidation of the compositions. Amounts of from 0.01% to 5.0% by weight are preferred.

The benzylureas may be prepared by any suitable method, and the three methods I have employed are indicated by the following reactions:

The reaction may ordinarily be carried out at room temperature. However, in some cases the reaction will be hastened by heating the reaction mixture.

The following examples typify the preparation of the benzylureas of this invention:

Example I.Reaction of benzyl chloride with arylurea 136 g. (1 mol) of phenylurea, 175 g. (1 mol) of alkylbenzyl chloride (average of 2 methyl and 0.5 ethyl groups per benzene ring) and 3 g. of iron powder were placed in a reaction vessel. The mixture was heated at -180 C. with continuous stirring for four hours. The material Was then cooled to room temperature and washed With water until it was free of chloride. The yield was 227 g. of a solid material melting over a range of 78-90 C. Percent nitrogen Was 7.6% (10% theoretical for l-(alkylbenzyl) -3-phenylurea).

Example II.Rcaclio;z of isocyanate and benzylamine 24 g. (0.2 mol) of phenylisocyanate and 21.0 g. (0.2 mol) of benzylamine were placed in a reaction vessel and stirred for one hour at room temperature. Then the resulting product was dissolved in isopropanol and recrystallized from the solution. The yield was 40 g. of a crystalline solidgvvhich melted at 172l'75 C. and had a nitrogen content of 12% (12% theoretical for l-benzyl-3-phenylurea).

The oxidation test was a modified version of the General Motors Oxidation Test, Type C. In the test, 300 ml. of the base fluid is placed in a tube, 2 /8 inches in diameter and 13 inches long. A glass air delivery tube is inserted into the sample tube. A coil consisting of 18 inches of ZS-gauge copper wire and 18 inches of 36-gauge iron wire is wound around the air delivery tube and immersed in the sample. The tube is heated to a temperature of 350 F. for a period of 150 hours, and during the test, 8 ml. per hour of watersaturated air is bubbled through the solution. At the end of the test, the increase in viscosity of the base fluid and the amount of pentane-insoluble material in the fluid are measured. Both of these values are indicative of the resistance of the lubricant to oxidation. The pentane insolubles in the original fluid are 0, and the increase in these materials represents products of oxidation.

The base fluid employed in the test was a neutral oilspray oil base containing 0.4% Zinc dialkylphosphorodithioate, 4% of an alkylmethacrylate-vinyl pyrrolidone detergent, and 1.5% of a polyisobutene viscosity index improver having an average molecular weight of about 120,000. The base fluid had an initial viscosity of 51 cs. at 210 F. In the test, a benzylurea antioxidant was compared with a conventional phenolic antioxidant. These data are summarized in the following table:

TABLE I i l Concen Pentane Viscosity, Antioxidant Additive tration, Insoluble, 210 F.

Weight Percent Increase, Percent Percent None 0. 13 51 l-alkylbenzyl-B-phenylurea (alkyl=average 2 methyl, 0.5 ethyl per benzyl group). 0. 1 0. 08 29 D0 h 0. 2 0. 07 31 Do 0. 4 0. 01 13 2,6'di(t-butyl) p-eresol 0. 4 0. 07 38 It can be seen from these data that the alkylbenzylurea reduced both pentane insolubles and viscosity increase to a much greater degree than the conventional antioxidant.

The grease tests which were employed were as follows:

The Bomb Oxidation Test, ASTM D94250, briefly involves subjecting a 20 g. sample of a grease to an initial pressure of 110 psi. of oxygen at 200 F. for 100 hours and measuring the pressure loss at the end of the period. Higher loss generally indicates greater oxidation of the sample. The bearing life test that was employed is known as the Navy High Speed Bearing Test and is described in Federal Test Method 331.1. In this test, a ball bearing was operated at 10,000 rpm. continuously for approximately 22 hours at 300 F. The apparatus was then cooled to room temperature during a period of 2 hours. This procedure of operating and cooling was repeated until there was bearing failure. Bearing Life is the number of hours to hearing failure.

Table II following shows the results of the above-mentioned tests. The base grease was a synthetic oil, bis-2- ethylhexylsebacate, thickened with by weight lithium stearate. The bearing life for each sample and the geometric mean of the bearing life (in parentheses) is given. Comparative data with a conventional zinc dithiocarbamate antioxidant is included.

These data show that lithium-based greases containing benzylureas are remarkably effective in increasing bearing life and are good antioxidants. Especially significant is the comparison with the commonly employed Zinc dithiocarbamate. This material, while showing good results in the bomb oxidation test (-3.3 psi. pressure drop), is quite ineffective in preventing bearing failure, giving only a l32-hour bearing life.

To further illustrate the effectiveness of the benzylureas in preventing corrosion, polyisobutenes containing the additives were subjected to a bomb test. The materials were subjected to the same temperatures and pressure as that previously described; however, the pressure was observed until there was a sharp decline in pressure rather than measuring pressure after a specified period. The polyisobutene was a material having an average molecular weight of about 950 and a viscosity of 1,050 SSU at 210 F. The antioxidant employed was the same alkylbenzyl phenylurea employed in the previous test. In the following table, the time to a sharp decrease in pressure is indicated as Induction Period measured in hours.

TABLE III Additive concentration, precent: Induction period, hr. 0 22 0.1 43 0.2 4S 1 0 500 As shown in the table, the benzylurea increases the induction period from 22 hours to over 500 hours at a 1% concentration. \lVhile conventional antioxidant, phenyl-anaphthylamine, has about a 500-hour induction period at concentration, this compound is volatile, quite toxic, and discolors the oil. The benzylurea has none of these disadvantages.

The oleaginous lubricants which comprise the bases for the compositions of this invention are those oily or greasy materials most commonly employed in lubrication. Examples of these maerials are natural and synthetic oils and greases made from these oils. Base materials which are not suitable for the compositions of this invention and are-not classified as oleaginous lubricants are those inorganic substances sometimes used in lubricating functions, such as molybdenum disulfide, tungsten disulfide, graphite, ground glass, ground basalt, etc.

The oils which can be used as base oils for the compositions of this invention include a wide variety of lubricating oils, such as naphthenic-base, paraffin-base and mixedbase lubricating oils, other hydrocarbon lubricants, e.g., lubricating oils derived from coal products, and synthetic oils, e.g., alkylene polymers (such as polymers of propylene, butylene, etc., and the mixtures thereof), alkylene oxide-type polymers (e.g., alkylene oxide polymers prepared by polymerizing alkylcne oxide, e.g., propylene oxide polymers, etc., in the presence of water or alcohols, e.g., ethyl alcohol), carboxylic acid esters (e.g., those which were prepared by esterifying such carboxylic acids as adipic acid, azelaic acid, suberic acid, sebacic acid, alkenylsuccinic acid, fumaric acid, maleic acid, etc., with the alcohols, such as butyl alcohol, hexyl alcohol, 2-ethy1hexyl alcohol, pentaerythritol, etc.), liquid esters of acids of phosphorus, alkylbenzenes, polyphenyls (e.g., biphenyls and terphenyls), alkylbiphenyl ethers, polymers of silicon (e.g., tetraethyl silicate, tetraisopropyl silicate, tetra(4- methyl-2-tetraethyl) silicate, hexyl (4-methyl-2-pentoxy) disiloxane, poly(methyl)siloxane, and poly(methylphenyl) siloxane, etc.

The base oils can be used individually or in combinations, wherever miscible or wherever made so by use of mutual solvents.

In addition to the inhibitors described in this invention, the lubricating compositions of this invention may also contain other lubricating oil and grease additives, such as oiliness agents, extreme pressure agents, oxidation inhibitors, rust inhibitors, corrosion inhibitors, viscosity index improving agents, dyes, lubricating oil detergents, etc.

I claim:

1. A lubricating composition comprising an oleaginous lubricant base and in an amount sufiicient to inhibit oxidation a benzyl-substituted urea of the formula:

wherein R is a phenyl radical or an alkylphenyl radical substituted by alkyl groups of l to 30 canbons and having a total of not more than 90 alkyl carbon atoms, and R R and R are hydrogen or hydrocarbyl radicals of 1 to 30 carbon atoms.

2. The composition of claim 1 wherein R is an alkylphenyl radical substituted by not more than 90 alkyl carbon atoms, R is hydrogen or alkyl group of 1 to 10 carbon atoms, and R and R are aryl or alkaryl radicals.

3. The composition of claim 2 in which the oleaginous lubricant base is a metal-soap thickened grease.

4. The composition of claim 3 in which the grease is a lithium soap thickened grease.

5. The composition of claim 2 in which R is an alkylphenyl group substituted by 1 to 3 alkyl groups containing a total of not more than 24 carbon atoms.

6. The composition of claim 5 in which R; and R are hydrogen and R is phenyl.

7. The composition of claim 1 in which R and R are hydrogen and R is benzyl.

8. The composition of claim 6 in which the benZyl-substituted urea is present in the amount of 0.01 to 5.0% by Weight.

References Cited UNITED STATES PATENTS 2,373,049 4/1945 Pedersen 44-74 2,477,872 8/1949 Haury 252403 X 2,683,081 7/1954 Hill et al. 44-71 DANIEL E. WYMAN, Primary Examiner. P. P. GARVIN, Assistant Examiner. 

1. A LUBRICATING COMPOSITION COMPRISING AN OLEGINOUS LUBRICANT BASE AND IN AN AMOUNT SUFFICIENT TO INHIBIT OXIDATION A BENZYL-SUBSTITUTED UREA OF THE FORMULA:
 2. THE COMPOSITION OF CLAIM 1 WHEREIN R IS AN ALKYLPHENYL RADICAL SUBSTITUTED BY NOT MORE THAN 90 ALKYL CARBON ATOMS, R1 IS HYDROGEN AND ALKYL GROUP OF 1 TO 10 CARBON ATOMS, AND R2 AND R3 ARE ARYL AOR ALKARYL RADICALS.
 3. THE COMPOSITION OF CLAIM 2 IN WHICH THE OLEAGINOUS LUBRICANT BASE IS A METAL-SOAP THICKENED GREASE.
 4. THE COMPOSITION OF CLAIM 3 IN WHICH THE GREASE IS A LITHIUM SOAP THICKENED GREASE. 